1. Field of the Invention
The invention concerns a device for monitoring the leakage of fluid from a component subjected to a pressurized fluid, and more particularly to a device for monitoring fluid leakage through a valve stem seal of a valve connected for controlling the flow of fluid in a pressurized fluid system.
2. Description of the Prior Art
In a pressurized water system, such as a pressurized water nuclear reactor, it is known to provide valves for controlling the flow of water in the system with leak-off connections between the primary and secondary valve stem packings. Water which leaks through the primary valve stem packing collects in a reservoir located between the primary and secondary packings of the valve stem and is drained off into a sump. Such drainage prevents a buildup of fluid pressure between the packings which could damage the secondary packing and result in leakage therethrough. In a pressurized water nuclear reactor this is particularly important in order to prevent radioactively contaminated water from escaping from an otherwise closed fluid system.
In a pressurized water system containing many valves, each having a leak-off connection, it is possible to determine the gross leakage of the system by measuring the amount of water flowing into the sump. An excessive flow into the sump could indicate that the primary packing on one of the valves is severely deteriorated. However, in such a system it is not possible to remotely assess the condition of any one valve. It is necessary to manually check each valve to determine which one is faulty. In a pressurized water reactor system, manual checking can be dangerous, because if the leakage through the primary packing becomes too great, the capacity of the reservoir between the packings could be exceeded. The resulting pressure against the secondary packing could cause contaminated water to leak through the secondary packing posing obvious health hazards.
It would therefore be desirable to be able to remotely assess the condition of each valve in the system on a continuing basis in order to prevent excessive leakage through the respective primary packings.
U.S. Pat. No. 3,276,246, issued to Truman et al, discloses a leakage detector for an oil wellhead wherein a vessel containing a float switch is disposed to collect oil leaking out of the top of the wellhead and accumulating between upper and lower packing glands. The float has a specific gravity lower than that of oil. As the level of the oil collecting in the vessel rises the float also rises. At a certain level the float activates a proximity switch which shuts down the wellhead motor. The vessel is provided with a weep hole for draining minor accumulations of oil and/or lubricant and a drain plug which can be manually removed to drain the vessel when significant amounts of oil are collected in the vessel. A problem with this device is that an excessive oil leak may cause the upper packing gland to fail if for some reason the float gets stuck or the motor fails to turn off in time before the vessel becomes completely filled with oil causing a back pressure against the upper packing gland.